Process for producing an alpha or beta-hydroxy acid-vinylpyrrolidone polymer, copolymer or graft polymer complex in the form of free-flowing powders having a high acid loading

Abstract

A process is provided for making a free-flowing powder of a complex of an alpha-hydroxy acid (AHA) and/or a beta-hydroxy acid (BHA) and a vinylpyrrolidone (PVP) polymer, copolymer or graft polymers, as the complexing agent, at high acid loadings, preferably 20-60% by weight. The presence of VP polymers, copolymers or graft polymers in the complex reduces the skin irritation effect of the acid when applied to the skin of the user. The process involves applying an aqueous solution or slurry of the acid to PVP, and, substantially immediately thereafter, evaporating the water to form a free-flowing powder of the complex of the acid and VP polymers, copolymers or graft polymers.

What is claimed is: 
     
       1. A process for the production of alpha or beta-hydroxy acid-vinylpyrrolidone (PVP) polymer, copolymer or graft polymer complexes in the form of free-flowing powders containing about 20-60% by weight of said acid and less than 2.5% by weight of water which comprises applying an aqueous solution or slurry of said acid to said PVP polymer, copolymer or graft polymer, substantially immediately thereafter, evaporating the water to form a free-flowing powder of the complex of the acid and said PVP polymer, copolymer or graft polymer having said composition. 
     
     
       2. A process according to claim 1 which comprises reacting a fluidized bed of PVP maintained at a reaction temperature of about ambient temperature to about 95° C. with finely divided droplets of a 20% to 88% by weight aqueous solution of said acid, and drying the product. 
     
     
       3. A process according to claim 2 wherein the acid feed rate is about 5-50 g/min/kg PVP. 
     
     
       4. A process according to claim 2 wherein the PVP is selected from water soluble and water-insoluble PVP powders in a range of molecular weights corresponding to the designation K-15 to K-120. 
     
     
       5. A process according to claim 1 wherein said PVP polymer is a water soluble PVP polymer. 
     
     
       6. A process according to claim 1 wherein said PVP polymer is a crosslinked PVP polymer. 
     
     
       7. A process according to claim 1 wherein said PVP is a copolymer of VP and vinyl acetate. 
     
     
       8. A process according to claim 1 wherein said PVP is a graft polymer of VP a C 1  -C 4  alkyl monomer. 
     
     
       9. A process according to claim 8 wherein said PVP is a graft polymer of VP and butene. 
     
     
       10. A process according to claim 1 wherein the product contains about 20-40% by weight acid. 
     
     
       11. A process according to claim 1 wherein the alpha-hydroxy acid is selected from lactic acid, glycolic acid, citric acid, tartaric or malic acid, and the beta-hydroxy acid is salicylic acid. 
     
     
       12. A process according to claim 1 wherein said process is carried out by spray or tray drying or in a fluidized bed. 
     
     
       13. A free-flowing powder of a complex of an alpha-hydroxy acid or a beta-hydroxy acid and a polyvinylpyrrolidone (PVP) polymer, copolymer or graft polymer complexing agent which contains about 20-60% by weight of said acid and less than 2.5% by weight of water. 
     
     
       14. A powder according to claim 13 wherein said alpha-hydroxy acid is lactic acid, glycolic acid, citric acid, tartaric acid or malic acid, and said beta-hydroxy acid is salicylic acid. 
     
     
       15. A powder according to claim 13 wherein said PVP is a water-soluble or water-insoluble PVP. 
     
     
       16. A powder according to claim 13 which contains about 0.1-2% by weight of a flow enhancer. 
     
     
       17. A powder according to claim 16 wherein said flow enhancer is fumed silica.